Active material and fluoride ion battery

ABSTRACT

A main object of the present disclosure is to provide an active material of which capacity properties are excellent. The present disclosure achieves the object by providing an active material to be used for a fluoride ion battery, the active material comprising: a composition represented by M 1 N X  in which M 1  is at least one kind of Cu, Ti, V, Cr, Fe, Mn, Co, Ni, Zn, Nb, In, Sn, Ta, W, and Bi, and x satisfies 0.05≤x≤3; or a composition represented by M 2 Ln y N z  in which M 2  is at least one kind of Cu, Ti, V, Cr, Fe, Mn, Co, Ni, Zn, Nb, In, Sn, Ta, W, and Bi, Ln is at least one kind of Sc, Y, and lanthanoid, y satisfies 0.1≤y≤3, and z satisfies 0.15≤z≤6.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.15/931,057, filed May 13, 2020, the contents of which are incorporatedherein by reference.

TECHNICAL FIELD

The present disclosure relates to an active material and a fluoride ionbattery.

BACKGROUND ART

As high-voltage and high-energy density batteries, for example, Li ionbatteries are known. The Li ion battery is a cation-based batteryutilizing the reaction of Li ions with cathode active materials, and thereaction of Li ions with anode active materials. Meanwhile, asanion-based batteries, fluoride ion batteries utilizing the reaction offluoride ions (fluoride anions) are known. For example, Non-PatentLiterature 1 discloses Cu as an active material used for a fluoride ionbattery.

CITATION LIST Non-Patent Literature

Non-Patent Literature 1: Le Zhang et al., “Study of all solid-staterechargeable fluoride ion batteries based on thin-film electrolyte”, JSolid State Electrochem (2017) 21:1243-1251

Summary of Disclosure Technical Problem

As the active material used for a fluoride ion battery, an activematerial with excellent capacity properties has been demanded. Thepresent disclosure has been made in view of the above circumstances anda main object thereof is to provide an active material of which capacityproperties are excellent.

Solution to Problem

In order to achieve the object, the present disclosure provides anactive material to be used for a fluoride ion battery, the activematerial comprising: a composition represented by M Nx in which M is atleast one kind of Cu, Ti, V, Cr, Fe, Mn, Co, Ni, Zn, Nb, In, Sn, Ta, W,and Bi, and x satisfies 0.05≤x≤3; or a composition represented byM²Ln_(y)N_(z) in which M² is at least one kind of Cu, Ti, V, Cr, Fe, Mn,Co, Ni, Zn, Nb, In, Sn, Ta, W, and Bi, Ln is at least one kind of Sc, Y,and lanthanoid, y satisfies 0.1≤y≤3, and z satisfies 0.15≤z≤6.

According to the present disclosure, usage of a specific metal nitrideallows an active material to have excellent capacity properties.

In the disclosure, the active material may comprise the compositionrepresented by the M¹N_(X).

In the disclosure, the M¹ may include at least one of Cu, Ti, Fe, and V.

In the disclosure, the active material may comprise the compositionrepresented by the M²Ln_(y)N_(z).

In the disclosure, the M² may include Mn.

In the disclosure, the Ln may include Ce.

The present disclosure also provides a fluoride ion battery comprising acathode active material layer, an anode active material layer, and anelectrolyte layer formed between the cathode active material layer andthe anode active material layer; wherein at least one of the cathodeactive material layer and the anode active material layer contains theabove described active material.

According to the present disclosure, usage of the above described activematerial allows a fluoride ion battery to have excellent capacityproperties.

Advantageous Effects of Disclosure

The present disclosure exhibits an effect of providing an activematerial with excellent capacity properties.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic cross-sectional view illustrating an example ofthe fluoride ion battery in the present disclosure.

FIG. 2 is the result of an XRD measurement for an active materialobtained in Example 3.

FIG. 3 is the result of a charge and discharge test for an evaluationbattery obtained in Example 1.

FIG. 4 is the result of a charge and discharge test for an evaluationbattery obtained in Example 2.

FIG. 5 is the result of a charge and discharge test for an evaluationbattery obtained in Example 3.

FIG. 6 is the result of a charge and discharge test for an evaluationbattery obtained in Comparative Example 1.

FIG. 7 is the result of a charge and discharge test for an evaluationbattery obtained in Example 4.

FIG. 8 is the result of a charge and discharge test for an evaluationbattery obtained in Example 5.

DESCRIPTION OF EMBODIMENTS

The active material and the fluoride ion battery in the presentdisclosure will be hereinafter described in details.

A. Active Material

The active material in the present disclosure is an active material tobe used for a fluoride ion battery, the active material comprising: acomposition represented by M¹NX in which M¹ is at least one kind of Cu,Ti, V, Cr, Fe, Mn, Co, Ni, Zn, Nb, In, Sn, Ta, W, and Bi, and xsatisfies 0.05≤x≤3; or a composition represented by M²Ln_(y)N_(z) inwhich M² is at least one kind of Cu, Ti, V, Cr, Fe, Mn, Co, Ni, Zn, Nb,In, Sn, Ta, W, and Bi, Ln is at least one kind of Sc, Y, and lanthanoid,y satisfies 0.1≤y≤3, and z satisfies 0.15≤z≤6.

According to the present disclosure, usage of a specific metal nitrideallows an active material to have excellent capacity properties. Forexample, Non-Patent Literature 1 discloses Cu as an active material usedfor a fluoride ion battery. When Cu is used as a cathode activematerial, the fluorination of Cu occurs during charge. A copper fluoridehas high insulation and thus its resistance increases along with chargeproceeds. In specific, when copper fluoride having high insulation isformed, electrons mainly supplied from a conductive material would havedifficulty conducting to the reaction site (interface between the metaland the metal fluoride). As a result, charge reaction would not proceedand enough capacity would not be obtained. Incidentally, in Non-PatentLiterature 1, although the diffusing distance of fluoride ions isreduced by thinning the shape of an electrode, the resistance is stilllarge and overvoltage is large as well. Because of the above, enoughcapacity is not obtained compared to the theoretical capacity.

To solve the problem, a specific metal nitride is used as an activematerial in the present disclosure. A positive hole is introduced whenthe metal nitride reacts with fluoride ions (when fluorine is doped),and thereby a semiconductor region is formed. This semiconductor regionhas a function of assisting electron conductivity, and thus theelectrons mainly supplied from the conductive material would be easilyconducted to the rection site (interface between the metal and the metalfluoride). As a result, it would be possible to inhibit the chargereaction from not proceeding, and thus the active material may haveexcellent capacity properties. Further, one of the advantages of themetal nitride is such that not easily affected by surface oxidationsince oxidation resistance and water resistance thereof are higher thanthose of a simple substance of metal. As a result, deterioration of theactive material due to factors such as generation of not-intended oxide,may not easily occur. Also, for example, when the active material in thepresent disclosure is used as a cathode active material, the firstcharge and discharge would be initiated from charge since the activematerial in the present disclosure usually does not contain a fluorineelement. For that reason, a metal fluoride which is more stable than asimple substance of metal may be used as an anode active material.

The active material in the present disclosure comprises, for example, acomposition represented by M¹N_(X).

In M¹NX, M¹ is at least one kind of Cu, Ti, V, Cr, Fe, Mn, Co, Ni, Zn,Nb, In, Sn, Ta, W, and Bi. The nitride of M¹ is known as asemiconductor. Also, M¹ may be just one kind of the aforementioned metalelements, and may be two kinds or more thereof. In M¹NX, x satisfies0.05≤x≤3. The x may be determined depending on the valence of M¹. Itmeans that the x may be the value with which the electrical neutralityis maintained.

It is preferable that M¹ contains at least one of Cu, Ti, V, Mn, Fe, Co,and Ni among the aforementioned metal elements. Also, the proportion ofthe specific metal element (M^(1x)) in M¹ is, for example, 50 mol % ormore, may be 70 mol % or more, and may be 90 mol % or more. M^(lx) isone of the metal elements Cu, Ti, V, Cr, Fe, Mn, Co, Ni, Zn, Nb, In, Sn,Ta, W, and Bi.

Examples of the active material comprising the composition representedby M¹N_(x) may include Cu₃N, TiN, Ti₂N, VN, MnN, Mn₂N, Mn₃N₂, Mn₄N, FeN,Fe₂N, Fe₃N, Fe₄N, Fe₈N, CoN, Co₂N, Ni₃N, and Ni₄N.

The active material in the present disclosure comprises, for example,the composition represented by M Ln_(y)N_(z). Since the fluoride of Lnhas high fluoride ion conductivity, the diffusibility of fluoride ionsimproves when the fluorination of the active material occurs. In MLn_(y)N_(z), M² is at least one kind of Cu, Ti, V, Cr, Fe, Mn, Co, Ni,Zn, Nb, In, Sn, Ta, W, and Bi. The nitride of M² is known as asemiconductor. Also, M² may be just one kind of the aforementioned metalelements, and may be two kinds or more thereof. Ln is at least one kindof Sc, Y, and lanthanoid. Any Ln is a metal element belonging to thethird group in the periodic table. Also, Ln may be just one kind of theaforementioned metal elements, and may be two kinds or more thereof.Also, there are no particular limitations on the kind of lanthanoid, andexamples thereof may include La, Ce, Pr, Nd, Sm, Eu, Gd, and Tb. InM²Ln_(y)N_(z), y satisfies 0.1≤y≤3, and z satisfies 0.15≤z≤6. The z maybe determined depending on the valence of M², and the valence andcomposition (y) of Ln. It means that the z may be the value with whichthe electrical neutrality is maintained.

It is preferable that M² contains at least one of Cu, Ti, V, Fe, Mn, Co,and Ni among the aforementioned metal elements. Also, the proportion ofthe specific metal element (M^(2x)) in M² is, for example, 50 mol % ormore, may be 70 mol % or more, and may be 90 mol % or more. M² is one ofthe metal elements Cu, Ti, V, Cr, Fe, Mn, Co, Ni, Zn, Nb, In, Sn, Ta, W,and Bi.

It is preferable that Ln contains at least one of Sc, Y, Ce, La, and Ndamong the aforementioned metal elements.

Also, the proportion of the specific metal element (Ln^(x)) in Ln is,for example, 50 mol % or more, may be 70 mol % or more, and may be 90mol % or more. Ln^(x) is one of the metal elements Sc, Y, andlanthanoid.

Examples of the active material comprising the composition representedby M²Ln_(y)N_(z) may include MnCe₂N₃, MnSr₃N₃, Fe₁₇Ce₂N₃, Fe₁₇Nd₂N₃,FeiVY₂N_(2.4), and BiLa₂N.

Examples of the shape of the active material may include a granularshape. The average particle size (D₅₀) of the active material is, forexample, 1 nm or more, and may be 5 nm or more. Meanwhile, the averageparticle size (D₅₀) of the active material is, for example, 30 μm orless, may be 10 μm or less, and may be 5 μm or less.

Incidentally, the average particle size (D₅₀) may be calculated from,for example, a measurement with a scanning electron microscope (SEM) ora transmission electron microscope (TEM). The number of samples ispreferably large; for example, it is 100 or more.

B. Fluoride Ion Battery

FIG. 1 is a schematic cross-sectional view illustrating an example ofthe fluoride ion battery in the present disclosure. Fluoride ion battery10 illustrated in FIG. 1 comprises cathode active material layer 1,anode active material layer 2, electrolyte layer 3 formed betweencathode active material layer 1 and anode active material layer 2,cathode current collector 4 for collecting currents of cathode activematerial layer 1, anode current collector 5 for collecting currents ofanode active material layer 2, and battery case 6 for storing thesemembers. In the present disclosure, at least one of the cathode activematerial layer 1 and the anode active material layer 2 contains theabove described active material.

According to the present disclosure, usage of the above described activematerial allows the fluoride ion battery to have excellent capacityproperties. Incidentally, in the present disclosure, just the cathodeactive material layer may contain the above described active material,and just the anode active material layer may contain the above describedactive material. Also, both of the cathode active material layer and theanode active material layer may contain the above described activematerial; however, in that case, among the above described activematerials, an active material with high reaction potential is used asthe cathode active material, and an active material with low potentialis used as the anode active material.

1. Cathode Active Material Layer

The cathode active material layer in the present disclosure is a layercontaining at least a cathode active material. In the cathode activematerial, usually, fluorination reaction occurs during charge anddefluorination reaction occurs during discharge. Also, the cathodeactive material layer may further contain at least one of a conductivematerial, a binder, and an electrolyte, other than the cathode activematerial.

It is preferable that the cathode active material layer contains theactive material described in “A. Active material” above as the cathodeactive material. In this case, an arbitrary active material with lowerreaction potential than that of the above described active material maybe used as the anode active material. On the other hand, when the activematerial described in “A. Active material” above is used as the anodeactive material, a general cathode active material may be used. Examplesof the general cathode active material may include a simple substance ofmetal, an alloy, a metal oxide, and fluorides of these.

There are no particular limitations on the conductive material if it hasdesired electron conductivity, and examples of the conductive materialmay include a carbon material. Examples of the carbon material mayinclude carbon black such as acetylene black, Ketjen black, furnaceblack and thermal black, graphene, fullerene, and carbon nanotube. Theproportion of the conductive material in the cathode active materiallayer is, for example, 1 weight % or more, and may be 5 weight % ormore. If the proportion of the conductive material is too little, thereis a possibility excellent electron conducting path may not be formed.Meanwhile, the proportion of the conductive material in the cathodeactive material layer is, for example, 20 weight % or less, and may be15 weight % or less.

If the proportion of the conductive material is too much, the proportionof the active material would be relatively little, and there is apossibility the energy density may decrease.

There are no particular limitations on the binder if it is chemicallyand electronically stable, and examples of the binder may include afluorine-based binder such as polyvinylidene fluoride (PVDF) andpolytetra fluoroethylene (PTFE). The electrolyte is in the same contentsas those described in “3. Electrolyte layer” later.

Also, the content of the cathode active material in the cathode activematerial layer is preferably larger from the viewpoint of capacity; forexample, it is 30 weight % or more, preferably 50 weight % or more, andmore preferably 70 weight % or more. Also, the thickness of the cathodeactive material layer is, for example, 0.1 μm or more and 1000 μm orless.

2. Anode active material layer

The anode active material layer in the present disclosure is a layercontaining at least an anode active material. In the anode activematerial, usually, defluorination reaction occurs during charge andfluorination reaction occurs during discharge. Also, the anode activematerial layer may further contain at least one of a conductivematerial, a binder, and an electrolyte, other than the anode activematerial.

It is preferable that the anode active material layer contains theactive material described in “A. Active material” above, as the anodeactive material. In this case, an arbitrary active material havinghigher reaction potential than that of the above described activematerial may be used as the cathode active material. On the other hand,when the active material described in “A. Active material” above is usedas the cathode active material, a general anode active material may beused. Examples of the general anode active material may include a simplesubstance of metal, an alloy, a metal oxide, and fluorides of these.

Regarding the conductive material, the binder, and the electrolyte, thesame materials described in the “1. Cathode active material layer” abovemay be used. Also, the content of the anode active material in the anodeactive material layer is preferably larger from the viewpoint ofcapacity; for example, it is 30 weight % or more, preferably 50 weight %or more, and more preferably 70 weight % or more. Also, the thickness ofthe anode active material layer is, for example, 0.1 μm or more and 1000μm or less.

3. Electrolyte Layer

The electrolyte layer in the present disclosure is a layer formedbetween the cathode active material layer and the anode active materiallayer. The electrolyte configured in the electrolyte layer may be anelectrolyte solution (liquid electrolyte), may be a polymer electrolyte,and may be an inorganic solid electrolyte.

The liquid electrolyte contains, for example, a fluoride salt and asolvent. Examples of the fluoride salt may include an inorganic fluoridesalt, an organic fluoride salt, and an ionic solution. Examples of theinorganic fluoride salt may include XF (X is Li, Na, K, Rb, or Cs).Examples of the cation of the organic fluoride salt may include an alkylammonium cation such as a tetramethyl ammonium cation. The concentrationof the fluoride salt in the liquid electrolyte is, for example, 0.1mol/L or more, may be 0.3 mol/L or more, and may be 0.5 mol/L or more.Meanwhile, the concentration of the fluoride salt is, for example, 6mol/L or less, and may be 3 mol/L or less.

Examples of the solvent may include a cyclic carbonate such as ethylenecarbonate (EC), fluoroethylene carbonate (FEC), difluoroethylenecarbonate (DFEC), propylene carbonate (PC), and butylene carbonate (BC);a chain carbonate such as dimethyl carbonate (DMC), diethyl carbonate(DEC), and ethyl methyl carbonate (EMC); a chain ether such as diethylether, 1,2-dimethoxy methane, and 1,3-dimethyoxy propane; a cyclic ethersuch as tetrahydrofuran and 2-methyl tetrahydrofuran; a cyclic sulfonesuch as sulfolane; a chain sulfone such as dimethyl sulfoxide (DMSO); acyclic ester such as γ-butyrolactone; a nitrile such as acetonitrile;and an arbitrary mixture of these. The polymer electrolyte may beobtained by, for example, adding a polymer to an electrolyte solutionfor gelling the solution.

Meanwhile, examples of the inorganic solid electrolyte may include afluoride of lanthanoid element such as La and Ce; a fluoride of alkalimetal element such as Li, Na, K, Rb, and Cs; and a fluoride of alkalineearth element such as Ca, Sr, and Ba. Also, it is preferable that theinorganic solid electrolyte is a fluoride that contains at least onekind of metal elements La, Ba, Pb, Sn, Ca, and Ce. The inorganic solidelectrolyte may contain just one kind of the aforementioned metalelements, and may contain two kinds or more thereof. Specific examplesof the inorganic solid electrolyte may include La_(1-x)Ba_(x)F_(3-x)(0≤x≤2), Pb_(2-x)Sn_(x)F₄ (0≤x≤2), Ca_(2-x)Ba_(x)F₄ (0≤x≤2), andCe_(1-x)Ba_(x)F_(3-x)(0≤x≤2). Each of the x may be larger than 0, may be0.3 or more, may be 0.5 or more, and may be 0.9 or more. Also, each ofthe x may be smaller than 1, may be 0.9 or less, may be 0.5 or less, andmay be 0.3 or less. There are no particular limitations on the shape ofthe inorganic solid electrolyte, and examples thereof may include agranular shape.

4. Other Constitutions

The fluoride ion battery in the present disclosure comprises at leastthe above described cathode active material layer, anode active materiallayer and electrolyte layer. Further, the battery usually comprises acathode current collector for collecting currents of the cathode activematerial layer and an anode current collector for collecting currents ofthe anode active material layer. Examples of the shape of the currentcollectors may include a foil shape, a mesh shape, and a porous shape.Also, the fluoride ion battery may comprise a separator between thecathode active material layer and the anode active material layer. Byarranging the separator, a battery with higher safety may be obtained.

5. Fluoride Ion Battery

The fluoride ion battery in the present disclosure may be a primarybattery and may be a secondary battery, but preferably a secondarybattery. The reason therefor is to be repeatedly charged and dischargedand useful as a car-mounted battery for example. Also, examples of theshape of the fluoride ion battery in the present disclosure may includea coin shape, a laminate shape, a cylindrical shape and a square shape.

Incidentally, the present disclosure is not limited to the embodiments.The embodiments are exemplification, and any other variations areintended to be included in the technical scope of the present disclosureif they have substantially the same constitution as the technical ideadescribed in the claims of the present disclosure and have similaroperation and effect thereto.

EXAMPLES Example 1

An active material (Cu₃N from RARE METALLIC Co., Ltd.), a solidelectrolyte (PbF₂ from Kojundo Chemical Laboratory Co., Ltd.) and aconductive material (acetylene black (AB), HS-100 from Denka CompanyLimited) were weighed so as to be Cu₃N:PbF₂:AB=30:60:10 in the weightratio, mixed by ball milling, and thereby a electrode mixture wasobtained. The obtained electrode mixture (working electrode), a solidelectrolyte (La_(0.9)Ba_(0.1)F_(2.9)) for forming a solid electrolytelayer, a mixture (counter electrode) in which a solid electrolyte (PbF₂from Kojundo Chemical Laboratory Co., Ltd.) and a conductive material(acetylene black (AB), HS-100 from Denka Company Limited) were mixed inthe weight ratio of PbF₂:AB=95:5, and a Pb foil werecompression-power-molded to obtain an evaluation battery.

Example 2

An evaluation battery was obtained in the same manner as in Example 1except that, in a working electrode, TiN (from Kojundo ChemicalLaboratory Co., Ltd.) was used as the active material andLa_(0.9)Ba_(0.1)F_(2.9) was used as the solid electrolyte.

Example 3

In an Ar glove box, a manganese metal (Mn) and a cerium metal (Ce) wereweighed so as to be Mn:Ce=1:2 in the molar ratio, crushed, and mixed.The obtained mixture was put in a quartz tube, vacuum drawn, and thenburned under nitrogen gas flow in the condition of at 900° C. and for 36hours. Thereby, an active material (MnCe₂N₃) was obtained. When an X-raydiffraction measurement using a CuKa-ray was conducted to the obtainedactive material, as shown in FIG. 2 , typical peaks of MnCe₂N₃ wereconfirmed in the vicinity of 2θ=32°, 34°, and 35°, which confirmed thatMnCe₂N₃ was obtained. An evaluation battery was obtained in the samemanner as in Example 2, except that MnCe₂N₃ was used as the activematerial in the working electrode.

Comparative Example 1

An evaluation battery was obtained in the same manner as in Example 1except that, in a working electrode, Cu was used as the active material.

[Evaluation]

Charge and discharge tests were conducted to the evaluation batteriesobtained in Examples 1 to 3 and Comparative Example 1. The conditions ofthe charge and discharge test in Example 1 were as follows: temperature:140° C., final potential in the working electrode: 0.3 V (vs Pb/PbF₂) to1.5 V (vs Pb/PbF₂), and current: 50 pA/cm². Also, the conditions of thecharge and discharge tests in Examples 2, 3, and Comparative Example 1were as follows: temperature: 140° C., final potential in the workingelectrode: −1.5 V (vs Pb/PbF₂) to 3 V (vs Pb/PbF₂), and current: 50μA/cm². The results are shown in FIG. 3 to FIG. 6 .

As shown in FIG. 3 , in Example 1 (Cu₃N), the plateau of dischargereaction was confirmed at about 0.6 V, and the plateau of chargereaction was confirmed at about 0.8 V. Also, it was confirmed that eachof a charge curve and a discharge curve had the plateau of two steps.Also, discharge capacity of approximately 650 mAh/g was obtained, whichwas close to the theoretical capacity (786 mAh/g). Also, as shown inFIG. 4 , in Example 2 (TiN), the plateau of discharge reaction wasconfirmed at about 0.2 V, and the discharge capacity of approximately 30mAh/g was obtained.

Also, as shown in FIG. 5 , in Example 3 (MnCe₂N₃), the plateau ofdischarge reaction was confirmed at about 1.4 V, and the plateau ofcharge reaction was confirmed at about 1.6 V, which means that thecharge and discharge reactions occurred at extremely high potentials.Also, the potential at which charge reaction occurred was close to thepotential at which discharge reaction occurred, and the overvoltage wassmall; thus, it was suggested that the battery reaction resistance waslow. This is presumably because, in addition to the fact that the effectof improving the electron conductivity was exhibited since the activematerial was nitride, the diffusibility of fluoride ions was alsoimproved since lanthanoid fluorides were generated.

Meanwhile, as shown in FIG. 6 , in Comparative Example 1 (Cu), thedischarge capacity did not reach at 20 mAh/g, which was drasticallylower than the theoretical capacity (843 mAh/g). The reason therefor waspresumably because the charge reaction did not proceed since thestructure in which the surface of the active material (Cu) was coveredwith an insulator (copper fluoride) was formed when charge started. As aresult, it is presumed that the discharge capacity drasticallydecreased. On the other hand, in Examples 1 to 3, it was confirmed thatthe active materials with excellent capacity properties were obtained byusing the specific nitrides.

Example 4

An evaluation battery was obtained in the same manner as in Example 1except that, in a working electrode, Fe₄N (from Kojundo ChemicalLaboratory Co., Ltd.) was used as the active material, andLa_(0.9)Ba_(0.1)F_(2.9) was used as the solid electrolyte.

Example 5

An evaluation battery was obtained in the same manner as in Example 1except that, in a working electrode, VN (from Kojundo ChemicalLaboratory Co., Ltd.) was used as the active material, andLa_(0.9)Ba_(0.1)F_(2.9) was used as the solid electrolyte.

[Evaluation]

Charge and discharge tests were conducted to the evaluation batteriesobtained in Examples 4 and 5. The conditions of the charge and dischargetests were as follows: temperature: 140° C., final potential in theworking electrode: −1.5 V (vs Pb/PbF₂) to 3 V (vs Pb/PbF₂), and current:50 μA/cm². The results are shown in FIG. 7 and FIG. 8 .

As shown in FIG. 7 , in Example 4 (Fe₄N), the plateaus of dischargereaction were confirmed at about −0.5 V and about −1.4 V, and thedischarge capacity of approximately 30 mAh/g was obtained. On the otherhand, as shown in FIG. 8 , in Example 5 (VN), a gentle curve wasobtained in the range of about 1.5 V to about −1.1 V in the dischargecurve, the plateau of discharge reaction was confirmed at about −1.1 V,and the discharge capacity of approximately 240 mAh/g was obtained.

Reference Sings List

-   -   1 cathode active material layer    -   2 anode active material layer    -   3 electrolyte layer    -   4 cathode current collector    -   5 anode current collector    -   6 battery case    -   10 fluoride ion battery

What is claimed is:
 1. A cathode active material layer to be used for afluoride ion battery, the cathode active material layer contains anactive material comprising: a composition represented by M¹N_(X) inwhich M¹ is at least one element selected from the group consisting ofCu, Ti, V, Cr, Fe, Mn, Co, Ni, Zn, Nb, In, Sn, Ta, W, and Bi, and xsatisfies 0.05≤x≤3; or a composition represented by M²Ln_(y)N_(z) inwhich M² is at least one element selected from the group consisting ofCu, Ti, V, Cr, Fe, Mn, Co, Ni, Zn, Nb, In, Sn, Ta, W, and Bi, Ln is atleast one element selected from the group consisting of Sc, Y, andlanthanoid, y satisfies 0.1≤y≤3, and z satisfies 0.15≤z≤6, wherein acontent of the active material therein is 30 weight % or more, and thecathode active material layer contains an inorganic solid electrolytehaving fluoride ion conductivity.
 2. The cathode active material layeraccording to claim 1, wherein the active material comprises thecomposition represented by the M¹N_(X).
 3. The cathode active materiallayer according to claim 2, wherein the M¹ includes at least one of Cu,Ti, Fe, and V.
 4. The cathode active material layer according to claim1, wherein the active material comprises the composition represented bythe M²Ln_(y)N_(z).
 5. The cathode active material layer according toclaim 4, wherein the M² includes Mn.
 6. The cathode active materiallayer according to claim 4, wherein the Ln includes Ce.
 7. The cathodeactive material layer according to claim 1, wherein the content of theactive material is 50 weight % or more.
 8. The cathode active materiallayer according to claim 1, wherein the content of the active materialis 70 weight % or more.
 9. A cathode active material layer to be usedfor a fluoride ion battery, the cathode active material layer containsan active material comprising: a composition represented by M¹N_(X) inwhich M¹ is at least one element selected from the group consisting ofCu, V, Cr, Fe, Mn, Co, Ni, Zn, Nb, In, Sn, Ta, W, and Bi, and xsatisfies 0.05≤x≤3; or a composition represented by M²Ln_(y)N_(z) inwhich M² is at least one element selected from the group consisting ofCu, Ti, V, Cr, Fe, Mn, Co, Ni, Zn, Nb, In, Sn, Ta, W, and Bi, Ln is atleast one element selected from the group consisting of Sc, Y, andlanthanoid, y satisfies 0.1≤y≤3, and z satisfies 0.15≤z≤6, and thecathode active material layer contains an inorganic solid electrolytehaving fluoride ion conductivity.
 10. The cathode active material layeraccording to claim 9, wherein the active material comprises thecomposition represented by the M²Ln_(y)N_(z).
 11. The cathode activematerial layer according to claim 9, wherein the M² includes Mn.
 12. Thecathode active material layer according to claim 9, wherein the Lnincludes Ce.
 13. The cathode active material layer according to claim 1,wherein the active material is Cu₃N or TiN.